U.S. patent application number 10/773391 was filed with the patent office on 2005-08-11 for apparatus and method for exercising a battery for an implantable medical device.
Invention is credited to Norton, John D., Schmidt, Craig L..
Application Number | 20050177198 10/773391 |
Document ID | / |
Family ID | 34826751 |
Filed Date | 2005-08-11 |
United States Patent
Application |
20050177198 |
Kind Code |
A1 |
Norton, John D. ; et
al. |
August 11, 2005 |
Apparatus and method for exercising a battery for an implantable
medical device
Abstract
Methods and apparatus of the invention include one or more of
the following: (a) a battery having an electrode that develops a
resistive film from inadequate discharge events, (b) a non- or
slowly-deforming capacitor capable of storing a charge from the
battery, the capacitor requiring no or few periodic battery
discharges for reforming oxide, (c) means for periodically
discharging the battery to reduce the film on the electrode, (d) a
lead for sensing physiologic electrical signals of a patient, (e) a
status system for monitoring cardiac activity of the patient, (f) a
therapy delivery system for delivering therapeutic electrical
energy to the patient, (g) a means for determining elapsed time
since a therapy delivery event occurred and/or battery discharge
adequate to remove film, (h) a means for optimizing battery
discharge, and (i) a means for optimizing the time between
discharging the battery.
Inventors: |
Norton, John D.; (New
Brighton, MN) ; Schmidt, Craig L.; (Eagan,
MN) |
Correspondence
Address: |
MEDTRONIC, INC.
710 MEDTRONIC PARKWAY NE
MS-LC340
MINNEAPOLIS
MN
55432-5604
US
|
Family ID: |
34826751 |
Appl. No.: |
10/773391 |
Filed: |
February 6, 2004 |
Current U.S.
Class: |
607/29 ;
607/27 |
Current CPC
Class: |
A61N 1/378 20130101;
A61N 1/3975 20130101 |
Class at
Publication: |
607/029 ;
607/027 |
International
Class: |
A61N 001/362 |
Claims
1. An implantable medical device for implantation into a patient,
comprising: a battery having an electrode that develops a resistive
film; a low deformation-rate capacitor capable of storing a charge
from the battery, the capacitor requiring few or no periodic
discharges of the battery for reformation; and means for
periodically discharging energy from the battery into the low
deformation-rate capacitor to reduce film buildup on the
electrode.
2. An implantable medical device according to claim 1, further
comprising a lead for sensing electrical signals of a patient via
at least one electrode operatively coupled to the lead.
3. An implantable medical device according to claim 2, further
comprising a status system for monitoring heart activity of the
patient through the lead.
4. An implantable medical device according to claim 3, further
comprising a therapy delivery system for delivering electrical
energy through the lead to a heart of the patient.
5. An implantable medical device according to claim 1, further
comprising a means for determining time elapsed since a therapy was
delivered to a patient or since the battery was at least partially
discharged.
6. An implantable medical device according to claim 1, wherein the
battery discharge is greater than about 2.5 Joules.
7. An implantable medical device according to claim 1, further
comprising a means for optimizing the battery discharge.
8. An implantable medical device according to claim 7, further
comprising a means for optimizing the time between discharging the
battery.
9. An implantable medical device according to claim 8, wherein the
means for optimizing the battery discharge is dependant upon
voltage delay.
10. An implantable cardioverter defibrillator comprising: a lead
for applying electrical energy to the patient; a battery having an
electrode for powering the implantable cardioverter defibrillator,
the battery having an electrode that develops a film on it over
time due to a lack of battery discharge; an ICD status system for
monitoring heart activity of the patient through the lead; a
therapy delivery system for delivering electrical energy through
the lead to a heart of the patient; a capacitor capable of storing
a charge from the battery, the capacitor requiring no periodic
discharges of the battery for reformation; and means for
periodically discharging the battery to reduce film buildup on the
electrode.
11. An implantable cardioverter defibrillator according to claim
10, further comprising a means for determining elapsed time since a
therapy was delivered to a patient or since the battery was
discharged to reduce film buildup.
12. An implantable cardioverter defibrillator according to claim
10, wherein the battery discharge is greater than about 2.5
Joules.
13. An implantable cardioverter defibrillator according to claim
10, further comprising a means for optimizing the battery
discharge.
14. An implantable cardioverter defibrillator according to claim
13, further comprising a means for optimizing the time between
discharging the battery.
15. An implantable cardioverter defibrillator according to claim
14, wherein the means for optimizing the battery discharge is
dependant upon voltage delay.
16. A method of exercising a battery of an implantable medical
device, comprising: determining whether a film is disposed on a
portion of an electrode of a battery; and discharging the battery a
sufficient amount to reduce the film disposed on a portion of the
electrode of the battery.
17. A method according to clam 16, further comprising: optimizing
energy used during exercising the battery.
18. A method according to claim 17, further comprising: optimizing
a time period, wherein said time period is defined as the amount of
time elapsed between consecutive exercising of the battery.
19. A method according to claim 17, wherein the energy used during
exercising the battery is optimized based upon voltage delay during
charging of a capacitor.
20. A method according to claim 17, wherein the energy used during
exercising the battery is optimized based upon discharging of the
battery.
21. A method according to claim 16, wherein the battery supplies
energy to a capacitor or an electrical resistor to exercise the
battery.
22. A method according to claim 21, wherein the capacitor charged
by the battery subsequently powers the device.
23. A method according to claim 16, wherein the battery is
discharged through a resistive load to exercise the battery.
24. A method of exercising a battery of an implantable cardiac
defibrillator, comprising: determining a period of time elapsed
since a cardiac therapy was administered to a patient or since a
battery exercising session was performed; resuming normal
implantable cardiac defibrillator operation if the last therapy or
exercising session was less than a predetermined amount of time;
and charging a capacitor with a predetermined amount of energy if
the last therapy or exercising session was performed a greater time
than the predetermined time.
25. A method according to claim 24, further comprising the step of
determining whether the cardiac therapy needs to be
administered.
26. A method according to claim 25, further comprising: instructing
a therapy delivery system to charge the capacitor to deliver the
cardiac on a scheduled basis.
27. A method according to claim 24, further comprising the step of
minimizing the amount of energy removed from the battery based on a
voltage delay.
28. A method according to claim 27, wherein a processor executes a
software module to optimize energy removal from the battery.
29. A method according to claim 24, further comprising the step of
minimizing the amount of energy removed from the battery based on a
capacitor charge time, wherein said capacitor charge time comprises
a period of time during which the capacitor is charged to a maximum
or rated voltage of said capacitor.
30. A method according to claim 29, further comprising the step of
determining whether the capacitor was charged to the maximum or
rate voltage of said capacitor.
31. A computer readable medium for storing instructions for
performing a method of exercising a battery of an implantable
cardiac defibrillator, comprising: instructions for determining a
period of time elapsed since a cardiac therapy was administered to
a patient or since a battery exercising session was performed;
instructions for resuming normal implantable cardiac defibrillator
operation if the last therapy or exercising session was less than a
predetermined amount of time; and instructions for charging a
capacitor with a predetermined amount of energy if the last therapy
or exercising session was performed a greater time than the
predetermined time.
32. A medium according to claim 31, further comprising instructions
for determining whether the cardiac therapy needs to be
administered.
33. A medium according to claim 32, further comprising instructions
for instructing a therapy delivery system to charge the capacitor
to deliver the cardiac on a scheduled basis.
34. A medium according to claim 31, further comprising instructions
for minimizing the amount of energy removed from the battery based
on a voltage delay.
35. A medium according to claim 34, wherein a remote processor
executes the instructions for optimizing energy removal from the
battery.
36. A medium according to claim 31, further comprising instructions
for minimizing the amount of energy removed from the battery based
on a capacitor charge time, wherein said capacitor charge time
comprises a period of time during which the capacitor is charged to
a maximum or rated voltage of said capacitor.
37. A medium according to claim 36, further comprising instructions
for determining whether the capacitor was charged to the maximum or
rated voltage of said capacitor.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of medical
devices. More particularly, the present invention relates to a
system for selectively exercising the battery of a battery-powered
medical device, such as an implantable cardiac defibrillator (ICD),
based on the charge delivery performance of the battery so as to
maintain charge delivery performance while conserving battery
energy.
BACKGROUND OF THE INVENTION
[0002] Medical devices are used to treat patients suffering from a
variety of conditions. Examples include implantable medical devices
(IMDs) such as implantable pacemakers and ICDs, which are
electronic medical devices monitoring the electrical activity of
the heart and, when necessary, providing therapeutic electrical
stimulation to one or more of the heart chambers. For example, a
pacemaker senses an arrhythmia episode (i.e., a disturbance in
heart rhythm) and provides appropriate therapeutic electrical
stimulation pulses, at a controlled rate, to selected chambers of
the heart in order to terminate the arrhythmia and restore the
proper heart rhythm. The types of arrhythmias detected and
corrected by pacemakers include bradycardia, which are unusually
slow heart rates, and tachycardia, which are unusually fast heart
rates.
[0003] Medical devices such as ICDs also detect arrhythmias and
provide appropriate electrical stimulation pulses to selected
chambers of the heart to correct the abnormal heart rate and/or
rhythm. In contrast to pacemakers, however, an ICD can also deliver
much stronger and less frequent pulses of therapeutic electrical
stimulation (e.g., cardioversion and/or defibrillation therapy).
This is because ICDs are generally designed to terminate episodes
of cardiac fibrillation (e.g., episodes of rapid, unsynchronized
quivering of one or more heart chambers) and severe tachycardia
(e.g., very rapid but relatively coordinated contractions of the
heart). To correct such arrhythmias, an ICD delivers a low,
moderate, and/or high-energy electrical therapy to the heart.
[0004] The typical defibrillator or cardioverter includes a set of
electrical leads, which extend from a sealed housing into operative
contact with a portion of a heart. Within the housing are a battery
for supplying power, one or more capacitors coupled to the battery
and adapted to rapidly deliver bursts of electric energy via the
leads to the heart, and monitoring circuitry for monitoring cardiac
activity and determining when, where, and what electrical therapy
to withhold or apply. The monitoring circuitry generally includes a
microprocessor and a computer readable memory medium storing
instructions not only dictating how the microprocessor answers
therapy questions, but also controlling certain device maintenance
functions, such as maintenance of the capacitors in the device.
[0005] With respect to ICDs, typically at least two capacitors are
electrically coupled to the heart. One type of capacitor adapted
for use in conjunction with an ICD includes aluminum electrolytic
capacitors, although other types have been used as well. This type
of capacitor usually includes sheets of aluminum foil and
electrolyte-impregnated separator material. Each strip of aluminum
foil is covered with an aluminum oxide, which insulates the foils
from the electrolyte in the paper. One maintenance issue with
aluminum electrolytic capacitors concerns the degradation of their
charging efficiency after long periods of inactivity. The degraded
charging efficiency, which stems from instability of the aluminum
oxide in the liquid electrolyte, ultimately requires the battery to
progressively expend more and more energy to charge the capacitors
prior to delivering cardioversion or defibrillation therapy.
[0006] Thus, to repair this oxide degradation, microprocessors are
typically programmed to reform the degraded (or deformed) aluminum
oxide. The capacitor reform process typically involves at least one
capacitor charge-discharge cycle. For example, an aluminum
capacitor is typically rapidly charged and held at or near a rated
or maximum-energy voltage (the voltage corresponding to maximum
energy) for a time period (e.g., on the order of less than about
one minute), before being discharged internally through a
non-therapeutic load. In some cases, the maximum-energy voltage is
allowed to leak off slowly rather than being maintained; in others,
it is allowed to leak off (or droop) for 60 seconds and discharged
through a non-therapeutic load; and in still other cases, the
voltage is alternately held for five seconds and drooped for 10
seconds over a total period of 30 seconds, before being discharged
through a non-therapeutic load. These periodic
charge-hold-discharge (or charge-hold-droop-discharge) cycles for
capacitor maintenance are referred to as "reforming."
Unfortunately, reforming aluminum electrolytic capacitors tends to
reduce battery life.
[0007] The aluminum electrolytic capacitors used in early ICDs
exhibited relatively low energy density (<2 J/cc) and therefore
contributed a large amount to the overall device volume. To
decrease capacitor and ICD volume, medical device designers,
suppliers and manufacturers developed implantable wet-tantalum
capacitors. In addition to having a higher energy density (>4
J/cc) such capacitors exhibit a slightly lower rate of
de-formation, and therefore require less energy to effectively
reform the oxide layer of the capacitor. More recently,
wet-tantalum capacitors that require very little or no reformation
have been developed. To wit, non-provisional U.S. patent
application Ser. No. 10/448,594 filed 30 May 2003 (Atty. Dkt.
P-11276.00) and entitled, "WET TANTALUM CAPACITOR USABLE WITHOUT
REFORMATION AND MEDICAL DEVICES FOR USE THEREWITH" and
non-provisional U.S. patent application Ser. No. 10/431,356 filed 7
May 2003 (Atty. Dkt. P-11277.00) entitled, "WET TANTALUM
REFORMATION METHOD AND APPARATUS" are directed to such subject
matters, and the contents of each are hereby entirely incorporated
by reference herein.
[0008] While substantially eliminating the need for capacitor
reformation, these low or non-reformation capacitors may contribute
to energy-management issues within an ICD. For example, capacitors
not requiring reformation can cause the ICD battery to operate
without a high current pulse for a long period of time (e.g.,
months to years). Most implantable device batteries are comprised
of Li/SVO (lithium/silver vanadium oxide), a lithium anode, and a
silver vanadium oxide cathode. When there is an extended period
between high voltage therapies or other high current events, the
battery can develop a deleterious resistive film on the surfaces of
an anode disposed within the battery. First, the lithium anode
forms its own passive film by reaction with electrolyte. This film,
commonly referred to as the solid electrolyte interface (SEI), is
typically harmless since it comprises an electrically conductive
film. However, the SEI film can increase in thickness over time,
and thus contribute increased electrical resistance to the
operative circuitry of an ICD.
[0009] Second, the SVO material also forms a film on the lithium
surface. This is equally undesirable as it results in further
increases in film thickness and in electrical resistance over time.
Generally, these problems are resolved during the reformation
process or as a result of one or more high current pulses, during
which the resistive film will dissipate (or "slough off") thus
providing a fresh lithium surface.
[0010] However, if an IMD uses a capacitor that does not require
reformation, then over time the above-mentioned SEI films can be
expected to only increase in size and electrical resistance. If
this occurs, subsequent high-current pulses will suffer from
"voltage delay" due to the increased resistance of the films.
Voltage delay occurs when the highly resistive SEI film causes the
voltage delivered during a high current pulse to be lower than a
desired magnitude (e.g., less energy than that which would be
delivered in the absence of resistive SEI film). This voltage delay
will occur until the film sloughs off the lithium. Voltage delay is
undesirable in that it causes the battery to take longer to charge
the capacitor and reduces battery life. For example, if the battery
voltage is lower during the high current pulse, it is delivering
less energy per unit time. Therefore, it takes more charge out of
the battery to provide the pulse and it takes longer to charge the
capacitor. This problem is exacerbated the longer the battery goes
without a capacitor reformation or a high current pulse.
[0011] Another problem is created if the battery voltage is too
low. In most ICDs there is a minimum voltage or a voltage floor
representing the voltage necessary to continue to power the ICD
circuitry while the capacitor is being charged. Generally, if the
battery voltage drops below this voltage floor, a power-on-reset
(POR) can occur where the ICD will suspend any therapy currently in
progress. To combat this problem ICDs will generally implement a
safety feature, which prevents the battery voltage from dropping
below the voltage floor by lowering the current drawn from the
battery when the battery voltage approaches the voltage floor.
However, by drawing less current from the battery the process of
charging the capacitor is lengthened. This is undesirable as it is
commonly accepted that the odds of survival or recovery from a
potentially lethal arrthymia such as ventricular fibrillation (VF)
decrease significantly as the amount of time taken to deliver a
cardiac therapy to terminate an episode of VF increases. A voltage
delay may exacerbate this problem in two ways. First, the voltage
delay would increase the time required to charge the capacitor by
reducing available battery power. Second, a voltage delay may cause
the battery voltage to drop below the voltage floor thus initiating
the POR safety feature, further reducing available battery power
and increasing capacitor charge time. This could potentially
prevent an appropriate therapy from even being administered as some
devices will either cease charging, or deliver a reduced energy
after a predetermined charge interval.
[0012] Yet another potential adverse impact of voltage delay is
reduced device longevity. Typically ICDs are designed to declare
the Elective Replacement Indicator (ERI) when the background
voltage of the battery (voltage in the absence of capacitor
charging) reaches a predetermined level. However, most devices
incorporate a secondary mechanism for declaring ERI when the
capacitor charge time reaches a predetermined, excessively high
level. In the event that voltage delay results in such an
excessively long charge time, these devices will trigger the ERI
well before battery depletion, significantly reducing the longevity
of the ICD. Therefore, a voltage delay not only delays the delivery
of a cardiac therapy it also has an impact on the overall device
operation.
[0013] In prior ICDs the energy required to reform the capacitor
was much greater than that required to remove the anode film from
the battery, and therefore dominated any increase in capacitor
charge time. Furthermore, the need to frequently reform the
capacitor provided the required periodic conditioning of the
battery necessary to minimize the effects of voltage-delay.
However, now that capacitors needing little to no reformation have
been developed, the potential exists for voltage-delay to become
substantial, resulting in extended capacitor charge times when long
periods of time pass between capacitor charging or other high
current drain events driven by the battery. Changing trends within
the industry may further exacerbate this. As ICDs have evolved,
detection algorithms and therapies have become more sophisticated.
As a result, devices are more frequently treating potentially fatal
arrhythmias with alternative low-energy therapies (e.g., so-called
anti-tachycardia pacing or "ATP"), thereby dramatically reducing
the number of high-energy therapies being administered. In
addition, indications for ICD implantation have been expanded to
include patients who are expected to require only very few
high-energy cardioversion or defibrillation therapies over the life
of the device.
BRIEF SUMMARY OF THE INVENTION
[0014] An implantable medical device in embodiments according to
certain embodiments of the invention may include one or more of the
following features: (a) a battery having an electrode that develops
a resistive film (b) a low deformation-rate capacitor capable of
storing a charge from the battery, the capacitor requiring few
periodic discharges of the battery for reformation, (c) a means for
periodically discharging the battery to reduce film buildup on the
electrode, (d) a lead for sensing electrical signals of a patient
through the lead, (e) a status system for monitoring heart activity
of the patient through the lead, (f) a therapy delivery system for
delivering electrical energy through the lead to a heart of the
patient, (g) a means for determining elapsed time since a therapy
was delivered to a patient or when the battery was discharged to
remove electrode film buildup, (h) a means for optimizing the
battery discharge, and (i) a means for optimizing the time between
discharging the battery.
[0015] An implantable cardioverter defibrillator according to one
or more embodiments of the present invention may include one or
more of the following features: (a) a lead for applying electrical
energy to the patient, (b) a battery having an electrode for
powering the implantable cardioverter defibrillator, the battery
having an electrode that develops a film on it over time due to a
lack of battery discharge, (c) an ICD status system for monitoring
heart activity of the patient through the lead, (d) a therapy
delivery system for delivering electrical energy through the lead
to a heart of the patient, (e) a capacitor capable of storing a
charge from the battery, the capacitor requiring no periodic
discharges of the battery for reformation, (f) means for
periodically discharging the battery to prevent film buildup on the
electrode, (g) a means for determining elapsed time since a therapy
was delivered to a patient or when the battery was discharged to
remove electrode film buildup, (h) a means for optimizing the
battery discharge, and (i) a means for optimizing the time between
discharging the battery.
[0016] A computer readable storage medium according to certain
embodiments of the present invention can include executable
instructions for performing one or more of the following: (a)
instructions for applying therapeutic electrical energy to a
patient via one or more electrical medical leads, (b) instructions
for powering an ICD with a primary battery cell, wherein the
battery cell develops an electrically resistive film over time due
to a lack of relatively high current drain (e.g., battery
discharge), (c) instructions for monitoring heart activity of the
patient through the medical electrical lead, (d) instructions for
operating a therapy delivery system adapted to deliver electrical
energy through a lead adapted to be coupled a patient's myocardium,
(e) instructions for storing electrical charge in a capacitor
delivered from the battery cell, wherein the capacitor requires
essentially no periodic discharges for capacitor reformation, (f)
means for periodically discharging the battery to prevent film
buildup on the electrode, (g) a means for determining elapsed time
since a therapy was delivered to a patient or when the battery was
discharged to remove electrode film buildup, (h) a means for
optimizing the battery discharge, and (i) a means for optimizing
the time between discharging the battery.
[0017] A method of exercising a battery for an implantable medical
device according to the present invention may include one or more
of the following steps: (a) determining whether a film may have
built up on an electrode of the battery, (b) discharging the
battery to reduce film build up on the electrode of the battery,
(c) optimizing energy used during exercising the battery, and (d)
optimizing the time period between exercising to extend the life of
the battery.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a simple block diagram illustrating an implantable
cardioverter defibrillator according to an embodiment of the
present invention.
[0019] FIG. 2 graphically depicts a battery voltage curve for a
battery operatively coupled to an implantable cardioverter
defibrillator over a time when a high current drain event occurred,
such as the battery charging a capacitor to deliver a high voltage
defibrillation therapy and the battery did not have a resistive
film disposed over an electrode thereof.
[0020] FIG. 3 graphically depicts a battery voltage curve for a
battery operatively coupled to an implantable cardioverter
defibrillator over a time when a high current drain event occurred
such as the battery charging a capacitor to deliver a high voltage
defibrillation therapy and a resistive film was disposed over at
least a portion of an electrode of the battery.
[0021] FIG. 4 depicts a process flowchart illustrating an
embodiment of the present invention for exercising a battery to
relieve the resistive film disposed on an electrode of the
battery.
[0022] FIG. 5 depicts a process flowchart illustrating another
embodiment of the present invention for exercising a battery to
relieve the resistive film disposed on an electrode of the
battery.
[0023] FIG. 6 depicts a process flowchart illustrating another
embodiment of the present invention for exercising a battery to
relieve the resistive film disposed on an electrode of the
battery.
[0024] FIG. 7 depicts a process flowchart illustrating yet another
embodiment of the present invention for exercising a battery to
relieve the resistive film disposed on an electrode of the
battery.
[0025] FIG. 8 depicts a process flowchart illustrating a further
embodiment of the present invention for exercising a battery to
relieve the resistive film disposed on an electrode of the
battery.
[0026] FIG. 9 graphically depicts a voltage curve for a battery
exercising pulse according to the present invention illustrating a
fiducial point indicative of the effective removal of a resistive
film from an electrode of the battery.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0027] The following discussion of the illustrated embodiments is
intended to enable a person skilled in the art to make and use the
claimed invention. Various modifications to the illustrated
embodiments will be readily apparent to those skilled in the art,
and the generic principles herein may be applied to other
embodiments and applications without departing from the spirit and
scope of the present invention as defined by the appended claims.
For example, those skilled in the art will appreciate that various
materials, components and system architectures may be used to
practice the invention. Accordingly, the present invention is not
intended to be limited to just the illustrated embodiments, but
should be accorded the widest scope consistent with the principles
and features disclosed herein as well as those inherent in the
subject matter described, as understood by those of skill in the
art. The following detailed description is to be read with
reference to the figures, in which like elements in different
figures have like reference numerals. The figures, which are not
necessarily to scale, depict selected embodiments and are not
intended to limit the scope of the invention. Skilled artisans will
recognize the examples provided herein have many useful
alternatives fall within the scope of the invention.
[0028] In general, the present invention applies to exercising a
primary or secondary battery cell that, for whatever reason, has
not recently discharged (e.g., delivered or drained) enough
electrical energy sufficient to remove a resistive film that
typically forms on at least a portion of an electrode thereof. Such
a film unfortunately produces delayed discharge thereby negatively
affecting rapid or high-rate discharge performance of the battery.
For certain battery applications such delayed discharge can
significantly and adversely affect the performance of electrical
circuitry powered by the battery. One such application involves
rapid charging one or high voltage capacitors operatively coupled
to an implantable cardioverter-defibrillator (ICD). Once fully
charged such capacitors must rapidly and precisely fully discharge
a potentially life-saving therapeutic cardioversion or
defibrillation charge through a defibrillation vector defined by a
pair of defibrillation electrodes disposed near a heart.
[0029] However, while the illustrations and written description
utilize the context of medical devices, the present invention
should not be construed as so limited. For example, while
cardioverter defibrillators, including ICDs, will benefit from the
teaching hereof, many various types of implantable and external
electronic and mechanical devices can advantageously utilize the
present invention. In the context of medical devices, any device
for treating patient medical conditions such as pacemakers,
defibrillators, neurostimulators, therapeutic substance delivery
pumps and the like can benefit from the present invention. For
purposes of illustration only, however, the present invention is
primarily described in the context of an ICD. In addition, while
the present invention is not limited to high-current-rate batteries
(high-rate batteries)--and may be utilized for low- or medium-rate
batteries--the present invention is described herein the context of
high-rate batteries coupled to one or more high voltage capacitors
and associated operative circuitry of an ICD.
[0030] With reference to FIG. 1, a simple block diagram
illustrating an ICD according to an embodiment of the present
invention, ICD 10 includes an ICD status system 12, implantable
leads 14, a therapy delivery system 16, a battery 18, and an
internal bus 20. ICD status system 12 includes a processor or
microcontroller 22 and a memory 24 with a software module 25.
Memory 24 stores several variables relating to patient monitoring,
capacitor performance, ICD performance, and the like, which are not
described in detail, as they are peripheral to the core of the
present invention. Memory 24 also stores several variables related
to battery performance including one of more of the following:
battery background voltage, battery loaded voltage, capacitor
charge time, time elapsed since last capacitor charge, time elapsed
since last battery exercise or conditioning, energy stored on the
capacitor during the last charging event, discharge conditions
during the last battery exercise or conditioning, other pertinent
measures of battery, capacitor and device performance and software
to perform various ICD functions including self-tests, algorithms
for patient monitoring, therapy delivery and the like. Memory 24
also includes software module 25, which performs battery-exercising
functions according to the present invention, which are discussed
in more detail below. It is contemplated that the software could be
replaced with hardware or firmware or combinations thereof. As
illustrated, processor 22 comprises a microprocessor with built in
memory; however, it is contemplated processor 22 could be a
microcontroller, an ASIC, or a pic controller within the context of
the present invention.
[0031] Implantable leads 14 include one or more medical electrical
conductive cardiac leads having electrodes operatively coupled
thereto (e.g., atrial or ventricular pace/sense electrodes,
defibrillation electrodes--not shown) as is known and used in the
art. One or more of the leads 14 are deployed into electrical
communication with a portion of myocardium and adapted to sense
and/or deliver therapeutic pacing stimulus. Leads 14 can be
deployed to an atrial or a ventricular epicardial site and/or an
atrial or ventricular endocardial site and configured for unipolar
or bipolar cardiac pacing and sensing.
[0032] For the exemplary ICD therapy delivery system 16 includes
one or more capacitors 26 and other circuitry (not shown) for
delivering or transmitting electrical energy from the battery 18 in
measured doses through leads 14 to the myocardium of a heart or to
other living tissue. Additionally, therapy delivery system 16
includes one or more timers, analog-to-digital converters,
transformers, and other conventional circuitry (not shown) for
conveying or measuring various electrical properties related to
performance, use, and maintenance of the therapy system. It is
contemplated capacitor(s) 26 could be any type of high voltage
capacitor, however, as illustrated capacitor(s) 26 comprise low- to
no-reformation capacitors such as wet-tantalum capacitors.
[0033] Generally, leads 14 sense atrial or ventricular electrical
activity and provide data representative of this activity to
monitoring system processor 22. Processor 22 processes this data
according to software instructions in memory 24. If appropriate,
processor 22 then directs therapy delivery system 16 to deliver one
or more measured doses of electrical energy or other therapeutic
agents through leads 14 to a patient's heart.
[0034] As used herein, battery 18 includes a single primary
electrochemical cell or cells. Battery 18 is volumetrically
constrained in the sense that the components in the case of battery
18 cannot exceed the available volume of the battery case. A
discussion of the various considerations in designing the
electrodes and the desired volume of electrolyte needed to
accompany them in, for example, a lithium/silver vanadium oxide
(Li/SVO) battery appears in U.S. Pat. No. 5,458,997 issued to
Crespi et al. Generally, however, the battery 18 must include the
electrodes and additional volume for the electrolyte required to
provide a functioning battery.
[0035] With reference to FIG. 2 which graphically depicts battery
voltage curve for a battery 18 operatively coupled to an ICD over a
time when a high current drain event occurred, such as the battery
18 charging a capacitor 26 to deliver a high voltage defibrillation
therapy and said battery 18 does not have a resistive film disposed
over an electrode thereof. The graph depicted in FIG. 2 shows a
voltage curve for a battery 18 operatively coupled to an ICD 10
over period of time wherein a therapy requiring a relatively
high-rate discharge of the battery 18. Basically, the graph
displays battery voltage over time with a dashed line representing
a voltage floor 30. The upper limit of the battery voltage is
indicated by an upper, substantially flat, line 32 illustrating the
average high voltage of battery 18 during operation of ICD 10. If
processor 22 detects the patient is in need of an electrical
therapy and then initiates therapy delivery, a signal is sent to
therapy delivery system 16 to rapidly charge capacitor 26. The
charging of capacitor 26 puts a large-drain load on battery 18 as
represented by downward curve 34 stemming from the upper line 32.
When capacitor 26 is charged to a desired maximum or rated voltage
the large-drain load ceases, as represented by point 36, and the
battery 18 begins to recover to the upper limit of battery voltage
32, as represented by upward curve 38. Notably, the graph depicted
in FIG. 2 represents a battery 18 absent any film buildup or a very
small film buildup as discussed above. Since there is a limited
film buildup, battery 18 is able to quickly provide the voltage as
required to rapidly and fully charge the capacitor 26. The total
time required for battery 18 to provide the full charge of
capacitor 26 and then recover is represented by .DELTA.t and the
total time required to supply voltage to capacitor 16 to provide a
therapy is represented by .DELTA.t'. Generally, it is desired for
.DELTA.t' to equal approximately 10 seconds or less to ensure
successful therapy delivery.
[0036] FIG. 3 graphically depicts a battery voltage curve for a
battery 18 operatively coupled to an ICD 10 over a time when a high
current drain event occurred such as the battery 18 charging a
capacitor 26 to deliver a high voltage defibrillation therapy when
a resistive film was disposed over at least a portion of an
electrode of the battery 18. That is, the graph depicted in FIG. 3
illustrates how the battery voltage varies over time when film is
present on an electrode thereof. Thus, FIG. 3 represents a common
situation wherein a film has grown on an electrode of battery 18.
Similar to the discussion above, if processor 22 detects the
patient is in need of an electrical therapy and then initiates
therapy delivery, a signal is sent to therapy delivery system 16 to
charge capacitor 26. Straight vertical line 40 represents the
situation where capacitor 26 has is receiving energy from battery
18; however, the resistive film acts to delay or block any
substantial energy transfer. Therefore, capacitor 26 quickly takes
the battery voltage to a low level, even beyond voltage floor 30 as
represented in FIG. 3. Fortunately, the rapid drain of energy from
the battery 18 operates to substantially remove the film from the
electrode. Thus, as the film begins to slough off the voltage of
battery 18 gradually begins to increase as represented by upwardly
curving line 42. Therefore, capacitor 26 has difficulty getting
charged rapidly because the resistive film reduces or impedes, at
least initially, the high-current drain from battery 18. In
addition, for certain ICDs a therapy delivery preserving circuit
can control or restrict energy transfer from battery 18 to
capacitor 26 (as represented by curve 42 in FIG. 3 as the voltage
rises above voltage floor 30). Once the voltage (i.e., as
represented by curve 42 rises above voltage floor 30, the therapy
delivery protection of the ICD ends and capacitor 26 can begin
fully charging once again. This phenomenon is represented by curve
42 leveling off above voltage floor 30. When capacitor 26 is
finished charging, as represented by fiducial point 44, battery 18
begins to recover to its full voltage (as depicted by substantially
horizontal line 32) as shown by upwardly curving line 46. The total
time required for battery 18 to charge capacitor 26 and then
recover is represented by .DELTA.t" and the total time required to
supply sufficient voltage to capacitor 16 to provide a therapy is
represented by .DELTA.t'". As can be seen from FIG. 3, it takes
substantially longer to charge capacitor 26 when one or more
electrodes of the battery 18 is covered by a resistive film than
not (as depicted in FIG. 2). This condition is highly undesirable
in the context of ICD operation--as well as certain other medical
and non-medical devices--as the longer it takes to prepare to
perform a time sensitive operation (e.g., deliver a high voltage
therapy), the less likely the operation will be successful. In the
context of an ICD, the higher degree of hemodynamic compromise and,
oftentimes, the lower the chances of successful defibrillation
and/or cardioversion therapy delivery. Further, the total charge
and recover time represented by .DELTA.t" is much longer as
well.
[0037] FIG. 4 depicts a process flowchart illustrating an
embodiment of the present invention for exercising a battery to
relieve the resistive film disposed on an electrode of the battery.
That is, FIG. 4 depicts a single embodiment of a battery-exercising
method according to the present invention. As stated above it is
undesirable to have a film build up in battery 18 as this can case
cause delay in performing an operation requiring a rapid drain of a
battery (e.g., charging a high voltage capacitor). As described and
depicted herein, the inventors have discovered that for certain
situations it is highly desirable to "exercise" a battery 18 to
prevent, or relieve any, film buildup within a battery 18. The
flowchart represented in FIG. 4 shows a simple embodiment of the
present invention where the battery exercising is somewhat
inflexible. To begin the battery exercising process, based on
sensed signals of cardiac depolarizations (or lack thereof)
processor 22 determines if a cardiac therapy is scheduled to occur
(as shown in FIG. 4 by state 48). If a cardiac therapy is
scheduled, processor 22 instructs therapy delivery system 16 to
prepare for delivery of said therapy (e.g., fully charge capacitor
26 in order to deliver the therapy). This prevents any battery
exercising from interrupting the timing of delivery of a
potentially crucial therapy. If a therapy is not scheduled, then
processor 22 proceeds to state 50 (which schematically represents a
timing utility or procedure). At state 50 processor 22 determines
how much time has elapsed since the last therapy was administered
to a patient or how long it has been since the most recent battery
exercising session. If less than a predetermined period of time
(e.g., three months) has elapsed since the most recent therapy
delivery or battery exercising, processor 22 resumes normal ICD 10
operation as represented in state 52. Processor 22 will then wait a
second predetermined time (e.g., one month) before returning to
state 48 to once again determine whether a therapy is needed before
determining when the last therapy or exercising occurred.
[0038] Generally, for certain ICD applications a three-month
timeframe is short enough so only a small amount of film buildup
will occur. Further, given a small amount of film buildup the
inventors posit that a relatively smaller amount of power is
required to exercise battery 18 to remove the film buildup than if
a heavy film had accumulated. However, the inventors fully
contemplate that a longer or shorter time frame for exercising the
battery could be utilized (e.g., one, six, nine twelve months)
without departing from the teaching of the present invention. At
these longer time intervals a chance exists that a patient might
require a high voltage therapy delivery before the exercising takes
place and therefore, there is a chance a larger film buildup will
be present in comparison to the three-month time interval. Further,
at longer time intervals the exercising of battery 18 will require
more power to relieve the electrode(s) of the film. With reduced
time frames a lower chance exists that a large film buildup will
occur; however, the more frequent exercising of battery 18 might
deplete battery 18 quicker than a longer time frame between
therapies and exercising. Optimizing the time intervals between
therapies and/or battery exercising based on the behavior of a
particular battery/device system tends to maximize the longevity of
a device while maintaining short therapy charge times.
[0039] If the time interval since a prior therapy or exercising is
greater than three months, then processor 22 instructs therapy
delivery system 16 to partially charge capacitor 26 with a
predetermined relatively low amount of energy relative to the
maximum or rated energy of a typical high voltage capacitor 26.
Thus, the capacitor 26 can be charged to about 2.5 J, as shown in
state 54. The inventors have found that 2.5 J of energy works well
at a three month time frame. However, it is fully contemplated any
relatively reduced amount of energy could be utilized without
departing from the spirit of the invention. Importantly, it is not
required for battery 18 to charge a capacitor 26 to perform the
battery exercising. In fact, a number of different ways exist to
perform the battery exercising of the present invention in an
energy efficient manner without utilizing any capacitor.
[0040] As noted above, the capacitor 26 need only be partially
charged (relative to a maximum or rated voltage of the capacitor)
since only a small amount energy drain is required to exercise
battery 18 to thereby recover its nominal film-free performance.
Therefore, during battery exercising battery 18 could charge
capacitor 26 to a very low energy as stated above, discharge
battery 18 through a non-therapeutic resistive load, or charge a
so-called ultra- or super-capacitor and slowly discharge such
capacitor to power a device (e.g., an ICD 10). The benefits of the
present invention are two-fold. First, battery 18 is maintained at
an optimal voltage level and second the amount of power used to
exercise battery 18 is minimal when compared to the power used to
reform a deformed or degraded dielectric oxide layer disposed in
and about the anode electrode of high voltage capacitors. If
processor 22 fully charges capacitor 26 to exercise the battery 18,
too much energy is used to exercise battery 18 than necessary to
improve the performance of the battery 18. Therefore, the present
invention allows for improved battery performance thereby providing
lower capacitor charge times, lower internal battery resistance,
and lower overall energy consumption--all without paying the high
price (or system energy cost) of fully charging capacitor 26. After
completing battery exercising operations, ICD 10 returns to state
52 from state 54 to resume normal ICD operation.
[0041] The battery exercising method represented in FIG. 4 is
somewhat inflexible in that the time frame and power for exercising
is set. More flexible battery exercising methods are discussed
hereinbelow, which are intended to introduce the uninitiated to
several related, alternate embodiments of the present invention.
Upon reflecting upon these embodiments those of skill in the art of
battery-powered devices will surely recognize other embodiments
and/or contemplate slight changes to the alternate embodiments. All
such embodiments are expressly deemed covered by this disclosure of
the present invention.
[0042] FIG. 5 depicts a process flowchart illustrating another
embodiment of the present invention for exercising a battery to
relieve the resistive film disposed on an electrode of the battery.
The battery exercising process depicted in FIG. 5 optimizes the
energy used to exercise and the timeframe between
exercising/therapies to extend the operating life of ICD 10.
Similar to the discussion above, the battery exercising process
first starts by determining if a cardiac therapy is scheduled
(including if an arrthymia detection sequence has been initiated)
as shown at state 60. If a therapy is scheduled (or detection
sequence underway), processor 22 instructs therapy delivery system
16 to fully charge capacitor 26 in order to deliver a therapy as
shown in state 62. If a therapy is not scheduled, then processor 22
proceeds to state 64. At state 64 processor 22 determines how long
it has been since the most recent therapy was administered to a
patient and how much time has elapsed since the last battery
exercising session. If the last therapy or exercising was less than
one month ago, processor 22 resumes normal ICD 10 operation as
represented in state 66. Processor 22 will then wait a
predetermined interval of time (e.g., three weeks) and then return
to state 60 to again determine whether a therapy is needed before
determining when the last therapy or exercising occurred.
[0043] If the most recent therapy delivery or battery exercising
occurred more than a predetermined amount of time ago (e.g., a
month or x-weeks), then processor 22 instructs therapy delivery
system 16 to partially charge capacitor 26 with a predetermined
amount of energy as represented in state 62. In the embodiment of
FIG. 5, processor 22 executes an optimization software module 25
(see FIG. 1) having algorithms, which minimize the amount of energy
removed from the battery 18 based on voltage delay. The software
module 25 can be based on several battery and capacitor charge
variables without departing from the teaching of the present
invention. For example, software module 25 could be based on
capacitor charge time, wherein if the charge time exceeds a certain
threshold, then the battery exercising voltage and/or the time
frame between exercising is modified. At state 68 processor 22
determines whether capacitor 26 was fully charged or if it was
charged with a smaller energy such at 2.5 J as discussed in the
embodiment of FIG. 4. If processor 22 determines the capacitor
charge was less than a full charge, then software module 25 returns
to state 66 and sets a longer exercising time, for example three
months. The process then begins again and if after three months no
therapy or battery exercising has occurred, then processor 22 once
again instructs battery 18 to apply a small charge to capacitor 26.
Software module 25 then determines whether a full charge was
administered and if not, then software module 25 returns to normal
ICD operation (at state 66).
[0044] Generally, software module 25 optimizes the amount of energy
removed from battery 18 through modification of the exercising
voltages and the time frames between exercising to determine
through experimentation the optimal exercising voltage and the
timing between battery exercising events. A conditioning discharge
event would be performed thus exercising the battery 18 at one
month, three month, six month, and twelve-month increments (or
other schedule) at a particular energy level for example a 2.5 J
pulse, a 15 J pulse, or a 32 J pulse (or the like). Then
periodically, a therapy is administered or the capacitor is fully
charged to measure the voltage delay. When the full charge is
discovered at state 68 software module 25 can then adjust the
interval between exercising at state 70 and/or the level of energy
for the exercising at state 72, based upon the measured voltage
delay. For example, if no voltage delay is detected, then software
module 25 can maintain the exercising voltage and extend the time
frame between exercising battery 18 and/or lower the exercising
voltage. If a voltage delay is detected, then the time frame
between exercising battery 18 could be lowered and/or the
exercising voltage could be increased. Software module 25 will then
track what exercising time frames are used and what exercising
voltages are being used to optimize the exercising process.
Software module 25 then stores the different amounts of energy
required depending upon how long it's been since the last pulsing
or the capacitor thus creating a map (e.g., data set or relational
database) for an optimum regime based on how a particular ICD 10
operates. Software module 25 insures the exercising treatment uses
as little energy as possible to optimize the total energy available
from battery 18 thereby potentially extending the operating life of
the ICD 10.
[0045] In addition, ICD 10 can be interrogated to obtain the data
set indicating the optimal battery exercising timeframes and
energy-release levels to be. Then, a next set of ICDs can be
programmed prior to implementation with an existing data set
storing exercising timeframe(s) and energy level(s) with reference
to the optimized timeframe(s) and energy level(s) and thereby
require less testing to employ near-optimal exercising timeframe(s)
and energy level(s) for a particular battery 18. A physician would
be able to program in the different energy levels and time frames.
Of course, while the present invention is described and depicted
herein as a part of medical device system having a single battery,
no such limitation should be inferred therefrom. Indeed, the
present invention hereby expressly claims such multi-battery device
systems, including such systems having more than one primary and/or
secondary batter operative coupled thereto.
[0046] FIG. 6 depicts a process flowchart illustrating another
embodiment of the present invention for exercising a battery to
relieve the resistive film disposed on an electrode of the battery.
As illustrated in FIG. 6, the process begins at initialization step
80 by setting a timer to a null (or a nominal value), 0, setting an
interval timer to null (or a nominal value), I.sub.o, and setting
an energy indicator to null (or a nominal value), E.sub.o. Then, at
step 82 normal operation of an ICD 10 begins as is known and
employed in the art. As before, at step 84 a determination is made
whether or not a therapy is scheduled (or an arrthymia detection
sequence is in process) and if affirmative, then a capacitor
charging process (and, as applicable, therapy delivery) occurs at
step 86 and the timer is reset to a null or nominal value at step
88 before resuming normal ICD operation at step 82. However, if no
therapy is scheduled (or being confirmed), then the process
proceeds to step 90 wherein the value of the interval timer is
evaluated. If the interval timer is not greater than the null (or
nominal value) then the process proceeds to step 82, normal ICD
operation. If the interval timer is greater than the null value
then the capacitor 26 is charged to a nominal energy value,
E.sub.o. As described herein, the process of nominally charging the
capacitor relieves the electrode of the layer of resistive film so
that the battery 18 will not suffer the discharge time delay in the
event that a high current drain event requires rapid discharge of
the battery 18.
[0047] FIG. 7 depicts a process flowchart illustrating yet another
embodiment of the present invention for exercising a battery to
relieve the resistive film disposed on an electrode of the battery.
As illustrated in FIG. 7, the process begins at initialization step
100 by setting a timer to a null (or a nominal value), 0, setting
an interval timer to null (or a nominal value), I.sub.o, setting an
energy indicator to null (or a nominal value), E.sub.o, and
defining a capacitor charging time as function of energy (e.g.,
CT.sub.max=f(E)). Then, at step 102 normal operation of an ICD 10
begins as is known and employed in the art. As before, at step 104
a determination is made whether or not a therapy is scheduled (or
an arrthymia detection sequence is in process) and if affirmative,
then a capacitor charging process (and, as applicable, therapy
delivery) occurs at step 118 and the timer is reset to a null or
nominal value at step 120 before resuming normal ICD operation at
step 102. However, if no therapy is scheduled (or being confirmed),
then the process proceeds to step 106 wherein the value of the
interval timer is evaluated. If the interval timer is not greater
than the null (or nominal value) then the process proceeds to step
102, normal ICD operation. If the interval timer is greater than
the null value then the capacitor 26 is charged to a nominal energy
at step 108 to a value, E.sub.o, and the time required to achieve
the nominal energy value is measured. Then, at step 110 the
measured charge time (CT) is compared to the value of CT.sub.max
and if CT exceeds CT.sub.max, then at step 112 either the energy is
increased from the nominal setting or the interval timer is
decreased to a new value (or both). However, if at step 110 the
value of CT does not exceed CT.sub.max, then the process proceeds
to step 114 wherein the energy is decreased from the nominal
setting or the interval timer is increased to a new value (or
both). Following performance of either step 112 or 114, the process
proceeds to step 116 and the timer is set of a null (or nominal
value) before returning to step 102, normal ICD operation.
[0048] As described herein, the process of nominally charging the
capacitor relieves the electrode of the layer of resistive film so
that the battery 18 will not suffer the discharge time delay in the
event that a high current drain event requires rapid discharge of
the battery 18.
[0049] FIG. 8 depicts a process flowchart illustrating yet another
embodiment of the present invention for exercising a battery to
relieve the resistive film disposed on an electrode of the battery.
As illustrated in FIG. 8, the process begins at initialization step
130 by setting a timer to a null (or a nominal value), 0, setting
an interval timer to null (or a nominal value), I.sub.o, and
setting a maximum charging time, CT.sub.max. The maximum charging
time can be set with reference to a maximum or rated voltage of one
or more capacitors operatively coupled to energize an ICD. Then, at
step 132 normal operation of an ICD 10 begins as is known and
employed in the art. As before, at step 134 a determination is made
whether or not a therapy is scheduled (or an arrthymia detection
sequence is in process) and if affirmative, then a capacitor
charging process (and, as applicable, therapy delivery) occurs at
step 150 and the timer is reset to a null or nominal value at step
152 before resuming normal ICD operation at step 132. However, if
no therapy is scheduled (or being confirmed), then the process
proceeds to step 136 wherein the value of the interval timer is
evaluated. If the interval timer is not greater than the null (or
nominal value) then the process proceeds to step 132, normal ICD
operation. If the interval timer is greater than the null value
then the battery 18 is exercised without utilizing a capacitor 26.
For example, at step 138 a battery 18 can be exercised by a rapid
albeit short, high-rate discharge distributed through a
non-therapeutic load, such an electrical resistor or by charging a
ultra- or super capacitor (not shown) either partially or fully. In
the latter case, the charge stored in the capacitor can be utilized
for carrying out various operations of the ICD 10. One such use can
involve providing sufficient power for short-term or extended
telemetry to a remote, external device. Alternatively, the power
can be used to provide pacing and/or sensing operations for low
power pacing therapy, or the like. In any event, while completing
step 138 the process proceeds simultaneously to step 140 wherein
the voltage of the battery 18 is monitored while the battery is
exercised to measure the amount of time elapsed until a declining
voltage is observed--during charging of the capacitor 26 (see FIG.
9 for additional details). Then, at step 142 the charging time,
expressed as CT, and comprising a time interval until declining
voltage is observed, is compared to the maximum charge time
(CT.sub.max). If the charge time, CT, is greater than the maximum
charge time CT.sub.max then the timing interval is increased at
step 146. And, if CT is less than CT.sub.max then the interval is
increased at step 144. In either event, after performing step 144
or 146 the time is reset of a null (or a nominal value) at step 148
before resuming normal ICD operation at step 132.
[0050] While not depicted or described with reference to the
foregoing illustrated processes, in the event that a comparison
renders an equivalent result, an indeterminate result is obtained.
Such a result may be handled in a number of ways; however, those of
skill in the art will recognize that such a result albeit unlikely
can be accommodated by returning to the prior step after a preset
time and re-executing the step that initially caused in the
indeterminate result.
[0051] FIG. 9 graphically depicts a voltage curve 160,162,164,170
for a battery exercising pulse according to the present invention
illustrating a fiducial point 168 indicative of the effective
removal of a resistive film from an electrode of the battery 18, as
briefly described with reference to FIG. 8, above. That is, FIG. 9
is a slightly more refined representation of the effects of and
morphology of an effective battery exercising pulse according to
the present invention. In FIG. 9, the time interval ("CT") denotes
the time during which the capacitor 26 is charged sufficiently to
remove the resistive film. Thus, as the resistive film is being
removed the portion 164 of the voltage curve of the battery 18
rises asymptotically to a fiducial point 166. As will be
appreciated by those of skill in the art this phenomenon indicates
that the current drain from the battery 18 is not being effectively
transferred to the capacitor 26. In this regard, compare FIG. 2 to
FIG. 9. That is, rather than falling in an exponential-like decay
over segment 164 of FIG. 9 (like segment 34 of FIG. 2), the battery
voltage actually rises. At fiducial point 166, the voltage of the
battery finally begins to decrease thereby indicating that the
capacitor 26 is more effectively absorbing charge from the battery
18. Then, when the capacitor 26 achieves its maximum or rated
voltage (at transition point 168) the voltage of the battery 18
rises rapidly (as illustrated by segment 170). Note that the
segment 170 is roughly equivalent to the segment 38 of FIG. 2,
which also indicates a fully charged capacitor 26 (albeit a
capacitor that never suffered charging performance difficulties due
to resistive film disposed on electrode of the battery 18).
[0052] It will be appreciated the present invention can take many
forms and embodiments. The true essence and spirit of this
invention are defined in the appended claims, and it is not
intended the embodiment of the invention presented herein should
limit the scope thereof.
* * * * *